1. Field of the Invention
The present invention relates to a piezoelectric speaker and a method of manufacturing the same, and more particularly, to a small piezoelectric speaker and a method of manufacturing the same that are capable of obtaining high sound pressure in a low frequency band and reducing distortion of sound.
2. Discussion of Related Art
A piezoelectric speaker has a smaller thickness, a greater weight and a lower power consumption than an existing voice coil motor (VCM)-type speaker. Accordingly, the piezoelectric speaker is widely used for small, thin and lightweight portable terminals.
Examples of a conventional piezoelectric speaker include a piezoelectric speaker with a piezoelectric vibrator, a piezoelectric speaker with a piezoelectric body, and a piezoelectric speaker with a piezoelectric film, as briefly described below.
First, in a conventional piezoelectric speaker, the piezoelectric speaker with a piezoelectric vibrator, as the piezoelectric vibrator vibrates, a diaphragm vibrates to generate sound. However, in the piezoelectric speaker having this structure, since the vibration of the piezoelectric vibrator must be delivered to the diaphragm via an elastic body for vibration delivery, the vibration of the piezoelectric vibrator must be very great and the diaphragm must be larger than the piezoelectric vibrator. Further, when the vibration is delivered, unnecessary resonance may occur, causing peak-dip of output sound pressure, and sound may be distorted, degrading sound quality.
In another conventional piezoelectric speaker, the piezoelectric speaker with a piezoelectric body attached on a metallic diaphragm, the metallic diaphragm is displaced by a signal applied to the piezoelectric body, so that sound is generated. The piezoelectric speaker having this structure can be manufactured in a smaller size than the piezoelectric speaker with a piezoelectric vibrator. However, it is difficult to reproduce sound in a low frequency band because the metallic diaphragm is thicker than the piezoelectric material. It is also difficult to embody a rich sound stage due to cool and sharp tones caused by a metal material of the metallic diaphragm. Further, since unnecessary resonance may be caused by a frame for supporting the metallic diaphragm, sound may be easily distorted.
In another conventional piezoelectric speaker, the piezoelectric speaker with a piezoelectric film such as polyvinylidene fluoride (PVDF), a conductive polymer film is formed on both sides of a thin piezoelectric film. A voltage is applied to electrodes formed around the conductive polymer film to generate sound. In this piezoelectric speaker, since a piezoelectric constant of the piezoelectric film is not great, small displacement occurs. Accordingly, the piezoelectric film must have a great size, such that the diaphragm is larger than for other conventional speakers.
It is difficult to make the conventional piezoelectric speakers in a small size because the piezoelectric speakers have large diaphragms and also to reproduce sound in a low frequency band due to their relatively thick diaphragms.
Further, in the conventional piezoelectric speakers, a standing wave is created by a structural symmetry between the piezoelectric thin film and the diaphragm, such that sound can be readily distorted.